HR: 09:00h
AN: V11E-05 INVITED    [Abstracts]
TI: Modeling stable isotope transport in metamorphic and hydrothermal systems
AU: * Baumgartner, L P
EM: Lukas.Baumgartner@unil.ch
AF: Institute of Mineralogy and Geochemistry, University of Lausanne, Lausanne, VD 1015, Switzerland
AU: Mueller, T
EM: mullet@rpi.edu
AF: Earth and Environmental Sciences, RPI, 110, 8th Street, Science Center, Troy, NY 12180- 3590, United States
AU: Skora, S
EM: Susanne.Skora@unil.ch
AF: Institute of Mineralogy and Geochemistry, University of Lausanne, Lausanne, VD 1015, Switzerland
AU: Begue, F
EM: Florence.Buegue@unil.ch
AF: Institute of Mineralogy and Geochemistry, University of Lausanne, Lausanne, VD 1015, Switzerland
AB: Stable isotopes are powerful tools for deciphering the fluid flow histories of metamorphic terrains. The nature of fluid flow, fluid sources, and fluid fluxes can be delineated in well constrained studies. Continuum mechanics models for stable isotope fluid-rock exchange were developed and used over the last three decades in an attempt to accurately interpret the signatures left behind by fluid flow in the earths crust. The efforts have been hampered by the realization that the exchange of many stable isotopes, e.g. oxygen and carbon, by intracrystalline diffusion, hence without re-organization of the crystal lattice, appears to be too slow to achieve significant exchange. This should lead to relatively flat isotopic exchange profiles on hand-, outcrop, or aureole scale. Nevertheless, isotopic fronts are typically sharp (sub mm to cm scale), when measured in the field. This has lead to the suggestion that these sharp fronts correspond to the sides of infiltration fronts, implying the data to have been collected at a high angle to the infiltration direction. Nevertheless, the fact that the oxygen and carbon fronts are located at the same place is not explained by this. A review of published carbon and oxygen data reveals that many contact aureoles show linear trends in oxygen-carbon isotope ratio diagrams for carbonate sample suits. This implies that the fluid composition infiltrating the aureoles had essentially an X(CO2) of 0.5. This is in contrast to skarn mineralogy developed, which requires a water-rich fluid, in agreement with the general notion that igneous fluids are water-rich. These and other observations indicate that the mass transport equation used for stable isotope exchange needs to be improved to model appropriately the actual isotope kinetics during fluid-rock exchange. Detailed isotope studies on systems where net transport reactions are driven by mass transport have led us to identify different exchange mechanisms, including: a) the stable isotope exchange is given by instantaneous mass balance written for the isotope during reaction; b) equilibrium precipitation of products, but slow exchange kinetics for reactants. These observations require that the reactive term in the stable isotope reactive transport equation is re-written to include the net transfer reactions, which in turn implies the solution of the transport equation for the elements driving the reaction.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1012 Reactions and phase equilibria (3612, 8412)
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting